Redox active coating on graphite surface of hierarchically porous wood electrodes for supercapacitor application

•A free-standing carbon electrode substrate with hierarchical pores derived from wood pellet was synthesized.•A graphite carbon network fabricated by an in situ catalytic graphitization has enabled fast ionic and electronic transport.•High energy, power capacity and cycling stability were demonstrated as assembled as an asymmetrical supercapacitor. A free-standing electrode with hierarchical pores and graphite surface is derived from wood pellet via a catalytic graphitization. The aligned microchannels of natural wood and the high conductivity of graphite has enabled fast ionic and electronic transport. The high porosity leads to a large surface area for the deposition of redox active materials. After an electrodeposition of Ni(OH)2 and Co(OH)2 on the graphitized wood, the electrode exhibits a high areal capacity without significant degradation in the electrochemical performance. An asymmetric supercapacitor, with a graphitized wood as the negative electrode and a Ni(OH)2/Co(OH)2 deposited wood as the positive electrode, shows a high areal capacitance of 2 409 m F/cm2, a high energy density of 0.75 mWh/cm2 at a power density of 0.750 mW/cm2. This high performance, free-standing and biodegradable wood-derived asymmetric supercapacitor demonstrates promising applications as energy storage devices.